A typical magnetic bubble memory is organized in a major-minor mode as first disclosed in U.S. Pat. No. 3,618,054, of P. I. Bonyhard, U. F. Gianola and A. J. Perneski issued Nov. 2, 1971. Such a memory includes a plurality of closed loop paths, called minor loops, in which bubble patterns move synchronously in response to a magnetic field reorienting in the plane of bubble movement.
Data is read out of the minor loops and written into the minor loops by means of an accessing path to which a bubble generator and a bubble detector are coupled. The accessing path comprises a bubble path or loop coupled to all the minor loops at reference positions at which the loop ends and associated stages of the major path or loop come into close proximity. An electrical conductor couples those positions in a manner to transfer or replicate a bubble pattern from, say, the minor loops to the major path or loop.
The organization of the major path or loop depends on whether a transfer or a replicate function is to occur between that path or loop and the minor loops. If a transfer function is to occur, that operation transfers the bubbles in the reference positions during a selected cycle of the in-plane field and leaves vacancies behind. The transferred pattern and the vacancies move synchronously in their respective paths or loops to return to the reference positions for movement of the transferred pattern, or an image thereof, back into the vacancies from which they originated. It is clear then that a transfer operation employs a major loop rather than a major path and that every transfer of a bubble pattern out of the minor loops is followed ultimately by a transfer of data back into the minor loops.
The major loop is organized differently when a replication function is performed at the reference positions. In that case, vacancies are not created when a bubble pattern moves to the major path. Rather an image of that pattern is produced by replication. Thus, the major path is a path and not a loop because the image need not be recirculated to be reunited with vacancies as is the case when transfer occurs.
The advantages of replication over transfer are well known. If replication is employed, data loss during power failures is a trivial problem because the data is still present in the selected memory address. Only the image can be lost. Further, replication permits faster operation because the image, once detected, may be destroyed rather than returned to vacancies. The latter operation requires considerable movement of data and occupies the major loop for a considerable time over that required for replication.
A further use for a replicate port is in the major path itself. For example, at present, destructive-read detector arrangements for ion-implanted bubble memories have better operating margins than nondestructive-read arrangements. But a destructive-read arrangement preceded by a replicate port operates as a nondestructive-read arrangement by generating an image of the data for return to the minor loops.
Commercially available magnetic bubble memories have major and minor paths defined by permalloy elements of the type disclosed in U.S. Pat. No. 4,014,009 of P. I. Bonyhard, Y. S. Chen and J. L. Smith issued Mar. 22, 1977. Such memories in which the paths are defined by ion-implantation are disclosed in U.S. Pat. No. 3,792,452, of M. Dixon, R. A. Moline, J. L. Horth, L. J. Varnerin, and R. Wolfe, issued Feb. 12, 1974. It is to magnetic bubble memories of the ion-implanted type that this invention is directed, the specific problem being that a replicate port for major-minor, ion-implanted bubble memories does not exist.
There is a good reason why replicate ports in such ion-implanted memories have eluded bubble circuit designers. Ion-implanted elements for moving magnetic bubbles in response to a reorienting magnetic in-plane field are characterized by charged walls which extend outwardly from the elements and thus cause bubble elongation also outwardly from the elements. But bubble replication, in permalloy circuits, has been performed by actively cutting a bubble which elongates along an edge of a permalloy element astride, for example, a portion of a conductor element which produces a (bubble-) collapsing field in response to the applied current. Unless the bubble extends across the conductor element, no such replication is possible. Unless each end of a bubble terminates on a strong attractive pole, bubble oscillation rather than replication occurs.
Replication functions often are implemented by electrical conductor patterns which are formed beneath the permalloy elements (in permalloy circuits) about which bubbles are elongated during bubble propagation in response to cycles of the in-plane field. Successful replication depends on proper placement of the conductors to produce cutting fields at a position across which a bubble is elongated (stretched). In this instance also, without strong poles on which to terminate, an elongated bubble merely oscillates rather than replicates. Certainly, at least an elongated bubble is not divided into two predictably, and certainly does not result in two bubbles at predictable positions.
With ion-implanted circuits, no anchoring of an elongated bubble appears possible. The reason for this is that one end of a charge wall extends like a spike outwardly from the propagation elements to occupy varying (rather than fixed) positions. Further, the end of the spike coupled to the propagation elements is mobile. Consequently, the positioning of a replicate conductor astride a bubble elongated by a charge wall has not led to successful replication.